Method of treating tricalcium phosphate



Patented May 9, 1933 UNITED STATES PArsNr orrics HAROLD E. WHITE,OF ZELIENOPLE, PENNSYLVANIA METHOD OF TREATING TRICALCIUM PHOSPHATE No Drawing. Original application filed February 9, 1928, Serial No. 253,228, now Patent No. 1,823,015, dated September 15, 1931. Divided and this application filed September 1Q, 1931. Serial No. 562,199.

This application is a division of that filed by me FebruaryQ, 1928, Serial No. 253,228, for a Method of treating tricalcium phosphate. 6 My present invention relates generally to the treatment of phosphate rock (tricalcium phosphate) and the production of phosphorus by means of such treatment Heretofore calcium sulphide has been prov 10 duced by various methods, one of such methods depending upon the reduction of calcium pulphate by means of carbon. Thishas been accomplished according to the following re- I action: oaso.+io=oas+ioo Another method of producing calcium sulphide has been accomplished by passing hydrogen sulphide gas over red hot lime accord- 2 ing to the following reaction:

Ca0 H S CaS H O The first above mentioned process requires a high temperature and is best performed in an electric furnace. The second above named process requires elaborate equipment and an expensive gas which must be first generated before the process is begun.

When the sulphides of the heavy metals to (such as lead sulphide, cuprous sulphides, zinc sulphide, iron sulphide and iron disulphide or iron pyrites) are roasted or smelted in order to get rid of the sulphur, the reaction causes much loss of heat since it is exothermic.

It has also been a practice of the art in the production of elemental phosphorus or phosphorus pentoxide to smelt phosphate rock (tricalcium phosphate). In this process it has been necessary first to reduce the phosphorus and flux the lime with a cheap acid, silica being generally used, which reacts acid at high temperatures.

. My invention utilizes the sulphur from one ofthe above described processes and the free lime from the otherin forming calcium sulphide, which is accomplished according to any one of the following reactions:

Irrespective of any of the intermediate reactions (that is, the reactions occurring between the beginning and the end of the method herein describedsuch,for example, as the formation of calcium carbide and /or calcium phosphide) the final result is the simultaneous production of calcium sulphide and phosphorus with a relatively small quantity of the metal or metallic phosphide, depending upon the character of the original sulphide used.

My invention is best carried out in a crucible type electric furnace which is provided with a roof and which can be maintained practically air tight. The furnace is under a slight vacuum so that the volatile products may be carried to the condensing apparatus and the gases disposed of to best advantage.

In carrying out my invention in such a furnace, the calcium sulphide, ferrophosphorus or lead or copper may be tapped 0d at regular intervals from the crucible and are easily separated by gravity While in theirv molten state.

Ordinary foundry coke may be employed as the source of carbon or the charge may be briquetted by using a coking coal or tar binder, the coal or tar, or a similar substance, then acting entirely or in part as the reducing agent.

When my invention is carried out as in the first above equation, the ferrophosphorus pentasulphide and ;.phosphorus 'itrisulpjh-ide according to the following reactions 9FeS eFe r isi sa P585 7F8S2 QFQZP PgS3 siaeejhowev 'r, tea disulphidebreaks up' intoiron sulphide and sulphurat a temperature below the formation point of ferrous phosphide, this reaction does not cause much trouble.

The economicaladvantages of'my process can readily" be seen. Whereas the sulphides I from smelting sulphide ores are largely Wasted or made into sulphuric acid, they can,

' by'means of'my invention, be safely dispose of and utilized to advantage.

In the manner thus above described, it is possible to producea substantially pure cal:

cium sulphide, As "is"Well"knovvn,"the 'c'onstitue'n'ts ofo' rdinary phosphate rock, besides tricalcium phosphate,-are chiefly iron onide, alumina, calcium fluoride, andsilica. The major portion of the iron-oxide is reduced and reports as ferrophos'phorus the alumina remains as aluminum sulphide, whil e the silica reports partly as silicon in *the ferrophosphorus and as silicon sulphide which is volatilized from the furnace. a

By means of my "invention I am able to economically; produce phosphorus as W611 as I In producing phosphorus,the. furnaceis charged with suitable quantitiesof "tricalcium phosphate. (phosphate rock) iron J sulphide (iron disulphide),coke orfits equivacollected in a gas'main leading from the furnace and then collected in a suitable coni denser. Care should be taken during the pro- In makingphosphoric acid means of my invention, the furnace is charged With jsuitablequ'antities of the tricalciumphosphate (phosphaterock), iron sulphide (or iron disulphide), coke'or' its equivalent, as'in the case of'the initial step in th e production of phosphorus. Duringthe reduction process for makingphosphor'ic acid, a suitable" Thus elemental phosphorus lowing reactions fl Placez a l-IP03 2HgE O (.pyrophosphoric ac1 2H;P O QH O II-1 1 0. (orthophosphoric acid) the final product.

7 l S 02 S02 The novel feature of this methodas' ap- 1 pliedto phosphoric acid" resides in the fact that "the phosphorus vapors and sulphur vapors do not'act in' the same manner, the

sulphur going'only' to'SO whereas it tak'es SO to"make"s'ulphuric'acid. "By reason of this fact; the two vapors can besepar'ated in f the Cott're'll precipitator and the S later oxidized and converted'to sulphuric acid. 'By means of my invention, it is, therefore, pos- V sible to use sulphide slags in the smelting of T tricalcium s phosphate (phosphate rock) Whether elemental phosphorus or phosphoric acid is produced.

l It'shoii-ldbeinoted that in carrying out my method, there is a 'la'rge amount'of carbon monoxide Whichre'sults from thereactions' set forth. If desired, this carbon monoxide can be disposed of commercially, or it may beused in my method' for preheating the stock and the blast. I

" In practicing my invention for the'manu-' facture of phosphoric acid, it is characterized by the fact that a relatively large v amount of sulphur is driv'en off from the I lent. Suificient'heatisthen applied to'produce the phosphorus and sulphur vapors or fumes, which vapors or fumes are suitably furnace charge alongwiththe phosphorus (especially if'iron disulphide is used as the source of the sulphur). The: sulphur burns to sulphur dioxide and the phosphorus to P 05. 'The latter is strongly hygroscopic,

While the former is Weakly'so. In the collection of phosphoric acid by means of the Cottrell electrical precipitator, the discharge from the Cottrell electrical'precipitator will be practically free from PgO and contain appreciable quantities of sulphur dioxide,

which later may be collected and manufac theneasily fusiblesulphides (such as alumi l.

num sulphide, potassium sulphide, or magnesuim sulphide) which form eutectics with calcium sulphide may be introduced into the slag.

In this way and by this selective precipitation phosphoric acid practically free from sulphuric or sulphurous acids may be obtained.

In carrying out my invention the quantities of ironadded to the furnace charge may be increased or decreased depending upon the proportion of ferrophosphorus and volatilized phosphorus desired.

Where it is desired to produce phosphoric acid, it is possible to use a fuel fired furnace such as a cupola or blast type furnace, and

thus take advantage of the large quantity of carbon monoxide generated by preheating the blast.

As is well known, the use heretofore of the fuel fired furnace or smelting phosphatic materials has been found to be uneconomical due to the large volume of practically worthless slag to be handled, the necessity of making it very acid so that it may be easily tapped and the resultant gummy nature of the stock due to the formation of a volatile siliceous slag which condenses in the stock and prevents the uniform escape of the gases.

By using my herein described process, the nature of the stock is so porous that gases easily filter through and, moreover, there is littlesticky slag present which condenses in the stock and plugs the pores thereof.

Having thusdescribed my invention, what I claim is:

1. A method of treating tricalcium phosphate by charging a furnace with suitable quantities of tricalcium phosphate, a heavy metal sulphide and coke, then excluding substantially all air from the furnace, then applying sufiicient heat to produce elemental phosphorus vapors and a calcium sulphide slag and to liberate the heavy metal from its sulphide, then separating the heavy metal from calcium sulphide slag while in the molten state, and then collecting the phosphorus vapors and condensing them where by elemental phosphorus is produced.

2. A method of treating tricalcium phosphate comprising the reduction of such phosphate in the presence of the sulphide of a heavy metal and coke, andtlien introducing easily fusible sulphides whereby the sulphide slag thus formed is suificiently fluid to permit proper separation of the metals from the slag.

In testimony whereof, I have hereunto signed my name.

HAROLD E. WHITE. 

